This function enables tracing:

 	Function:	IO$_LD_CONTROL

 	P1 = number of trace buffer packets to allocate
 	P6 = Subfunction: LDIO$K_ENABLE_TRACE

 	IOSB word 0 = status

 	To reset the tracebuffer the additional subfunctionmodifier
 	LDIO$M_RESET can be specified. No new tracebuffer will be
 	allocated when that is done.

 	Requests for FDT tracing need to add the subfunctionmodifier
 	LDIO$M_FDTTRACE.

 	Requests for accurate timing tracing need to add the
 	subfunctionmodifier LDIO$M_ACCURATE.

 	Specifying LDIO$M_TRACE_ALL will enable tracing of requests
 	going to the container file as well (tapes only).

 	Errors returned:

 	SS$_ACCVIO	Parameter cannot be read
 	SS$_BADPARAM	Zero buffer size specified
 	SS$_EXBYTLM	Exceeded BYTLM quota for the process
 	SS$_INSFMEM	Not enough memory to allocate trace buffer
 	SS$_TOOMUCHDATA	Trace is already active
 	SS$_NORMAL	Successful completion